Thin films are vital to the operation of many integrated optic and optoelectronic devices. Thin film ion-conductive coatings are currently employed within electrochromic devices and solid state storage batteries as described, for example, in U.S. Pat. No. 4,832,463. These devices basically consist of a number of transparent optical films deposited on a transparent substrate such that the properties of the optical films such as thickness, index of refraction and absorption must be carefully controlled. One method for determining such optical properties is to employ the optical film sample as one beam-splitter within an optical interferometer as described in the paper entitled "Optical Parameters of Partially Transmitting Thin Films" by J. Shamir and P. Graff, published in the Applied Optics, December 1985, Volume 14, No. 12. The use of the optical film sample as one of the beam-splitters, however, requires manual beam alignment procedures that are difficult to achieve. Since the accuracy of the measurements strongly depends on the uniformity of the interference patterns developed, non-uniformity of the optical film sample or of the other optical components could lead to ambiguous results. Phase conjugate mirrors as one means of correcting phase distortions in an optical laser cavity is described within U.S. Pat. No. 4,529,273. The use of phase conjugate mirrors within other such optical devices is described within U.S. Pat. No. 4,280,764; 4,718,749 and 4,773,719. When the electrochromic devices described in the aforementioned U.S. Patents are considered for commercial utilization, such precision manual alignment would render interferometric evaluation extremely difficult and economically infeasible. One object of the instant invention is to provide apparatus which automatically provides beam alignment while compensating for any non-uniformity of both the optical films and the accompanying optical components.